Enhanced A12O3-Ti(C,N) multi-coating deposited at low temperature

ABSTRACT

A coated body having a multi-layer of κ-Al 2 O 3  and or γ-Al 2 O 3  or TiN applied by MTCVD (Medium Temperature Chemical Vapor Deposition) is disclosed. The multi-layers can be interspersed with layers of Ti(C,N) which can also be applied by MTCVD. The body which is coated is preferably a cemented carbide, cermet, ceramic and/or high speed steel and may be used as a metal cutting insert.

BACKGROUND OF THE INVENTION

[0001] Multi-layers of κ-Al₂O₃ and Ti(C,O) or κ-Al₂O₃ and TiN have proved to exhibit better wear properties than single oxide layers, see U.S. Pat. No. 5,700,569 and U.S. Ser. No. 09/717,006.

[0002] The deposition process of these prior art multi-layers is, however, relatively long and deposition is usually carried out at relatively high temperatures (usually at about 1000° C.), resulting in the transformation of kappa-alumina to alpha-alumina. The volume shrinkage encountered in the phase transformation will reduce adhesion of the alumina layers. As a result, adhesion problems in production will occur.

[0003] It has usually been thought that deposition temperatures of about 1000° C. or higher are needed to deposit Al₂O₃ coatings. As shown in the recent U.S. application Ser. No. 09/498,344, Al₂O₃ can be deposited at the deposition temperatures about or exceeding 800° C., but less than 1000° C. Further, it was shown that the two Al₂O₃ phases, κ and γ, could be deposited in a controlled way.

[0004] It has recently been confirmed that Ti(C,N) exhibits better wear resistance against crater wear and flank wear in hypoeutectoid steels than TiN (U.S. Ser. No. 09/207,687). In recent in-house cutting tests, it has also been found that in hypereutectoid steel, Ti(C,N) is better that TiN, especially with respect to flank wear. In hyper-eutectic steel, Al₂O₃ is a superior coating material against crater wear. In recent cutting tests in-house, it has also been found that the adhesion of both κ and γ phases to the MTCVD Ti(C,N) deposited at 800° C. is surprisingly good. By depositing κ or γ with MTCVD Ti(C,N) as a multi-layer, the wear properties of the prior art TiN/Ti(C,O)-κ multi-layers could thus be enhanced.

OBJECTS AND SUMMARY OF THE INVENTION

[0005] It is an object of this invention to avoid or alleviate the problems of the prior art.

[0006] It is further an object of this invention to provide enhanced wear properties of TiN/Ti(C,O)-κ multi-layers by depositing κ or γ with MTCVD Ti(C,N) as a multi-layer.

[0007] In one aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of γ-Al₂O₃.

[0008] In another aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of κ-Al₂O₃ and/or γ-Al₂O₃ layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N).

[0009] In another aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of κ-Al₂O₃ and γ-Al₂O₃, each applied by a chemical vapor deposition at a temperature of from 700 to 900° C.

[0010] In another aspect of the invention there is provided a coated body wherein the coating comprises a multi-layer of κ-Al₂O₃ and/or γ-Al₂O₃ layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N).

[0011] In yet another aspect of the invention there is provided a coated body wherein the coated comprises a multi-layer of κ-Al₂O₃ and/or γ-Al₂O₃ layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N) and with a layer of Ti(C,N) atop of the said multi-layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a representation of a coated body of the present invention including κ-Al₂O₃ multi-layers (FIG. 1a), γ-Al₂O₃ with multi-layers (FIG. 1b) and a mixed γ- and κ-Al₂O₃ multi-layer (FIG. 1c).

[0013]FIG. 2 is a representation of a coated body of the present invention useful in cutting of SS1672 (FIG. 2a) and SS2258 (FIG. 2b).

[0014]FIG. 3 shows Scanning Electron Microscope (SEM) images of the cutting edges of single and multi-layer κ-Al₂O₃ coated inserts after turning of 2, 5 and 8 minutes (9 minutes for the multi-layer κ-Al₂O₃ coated insert) of SS2258.

[0015]FIG. 4 shows Scanning Electron Microscope (SEM) images of the cutting edges of single and multi-layer κ-Al₂O₃ coated inserts after turning of 2, 9 and 15 minutes of SS1678.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0016]FIG. 1 shows a schematic of the coating layer according to this invention. The coating is composed of the following layers:

[0017] 1. MTCVD Ti(C,N) base layer, deposition temperature 800-900° C.

[0018] 2. Multi-layer structure consisting of κ-Al₂O₃ (FIG. 1a), γ-Al₂O₃ (FIG. 1b) or both (FIG. 1c), together with MTCVD Ti(C,N) interlayers, all deposited at a temperature of 800-900° C. The wear properties of γ are not yet fully elucidated. However, γ is a less stable phase than κ and can be used only in the uppermost layers of the multi-coating structure which will be subjected to the shortest annealing during deposition.

[0019] The Al₂O₃ layers in the multi-layer (whether γ or κ) have an individual thickness of from about 0.1 to 3.2 microns, preferably about 0.3 to 1.2 microns. The Ti(C,N) layers in the multi-layer have an individual thickness of from about 0.1 to about 3.2 microns, preferably from about 0.3 to about 1.2 microns. The total thickness of the multi-layer is from about 3 to about 30 microns, preferably from about 5 to 15 microns. The multi-layer may also be deposited onto a Ti(C,N) layer of from about 2 to about 15 microns, preferably from about 3 to 10 microns, which in this instance is the first layer applied onto the body. In addition, a Ti(C,N) layer of the same thickness can be deposited atop the outermost layer of the alumina.

[0020] The body is preferably formed of a cemented carbide, a cermet, a ceramic, or a high speed steel and the coated body is preferably used as a cutting tool in metal cutting operations.

[0021] The γ- and κ-Al₂O₃ layers as well as the Ti(C,N) layers are applied by MTCVD (Medium Temperature Chemical Vapor Deposition). The deposition of the γ- and κ-Al₂O₃ layers utilize the technique described in my copending U.S. patent application Ser. No. 09/498,334, herein incorporated by reference. In that process, H₂S is added to the otherwise conventional MTCVD techniques and apparatus in amounts greater than 0.7 vol %, generally 0.75 to 1.7 vol %, preferably greater than 1 up to about 1.5 vol %, of the total gaseous mixture.

[0022] The coating process is performed at temperatures of from about 700 to 900° C., preferably 750 to 850° C., at a pressure of from about 50 to 600 mbar, preferably from about 100 to 300 mbar, for a time sufficient to form the coating, generally from about 2 to 10 hours, preferably from about 4 to 8 hours.

[0023] It should be noted that the deposition of Al₂O₃ can be carried out at the same temperature as the MTCVD (Ti(C,N) layers, resulting in considerably shorter processes (the heating up/cooling down steps are eliminated) and the deposition of the multi-layer is carried out at relatively low temperature, resulting in no phase transformations. As a result, enhanced adhesion will be obtained and production yield will be enhanced. The multi-layer coating can be composed of both κ and γ which can simply be controlled by H₂S. The γ phase which is less stable than κ should be situated in the uppermost part (i.e., top half) of the multi-coating layer, if used; and as shown earlier, MTCVD Ti(C,N) exhibits better wear resistance than TiN. By using Ti(C,N) instead of TiN, crater wear resistance in hypo-eutectic steels and flank wear resistance in hyper-eutectic steels will be enhanced.

[0024] The invention is additionally illustrated in connection with the following Examples which are to be considered as illustrative of the present invention. It should be understood, however, that the invention is not limited to the specific details of the Examples.

EXAMPLE 1

[0025] Tables 1 and 2 show a summary of the wear properties of different coating in SS1672 and SS2258 (hypo- and hyper-eutectic steels, respectively) TABLE 1 SS1672 Crater Wear Flank Wear Notch Wear Deformation α-Al₂O₃ − − − − − − + + + + κ-Al₂O₃ − − − − − − + + + + + TiCN + + + + + − − (MTCVD) TiCN (CVD) + + + + + + − − TiN (CVD) + + + + + − − TiC (CVD) + + + + − −

[0026] TABLE 2 SS2258 Crater Wear Flank Wear Notch Wear Deformation α-Al₂O₃ + + + − − + + + + κ-Al₂O₃ + + + − + + + + + TiCN − − + + + − − (MTCVD) TiCN (CVD) − − + + + − − TiN (CVD) − − + − − − TiC (CVD) − − − + + + − −

[0027] As can be seen, the coating material may show very different behaviors in these steels. Consequently, different coating structures have to be developed for SS1672 (thin Al₂O₃ layers+thick Ti(C,N) layers, FIG. 2a) and for SS2258 (thick Al₂O₃ layers+thin Ti(C,N) layers, FIG. 2b) in accordance with the knowledge of the skilled artisan. Schematics of the optimized coating structures for these steel are shown in FIGS. 2a and 2 b.

EXAMPLE 2

[0028] Cutting tests were performed in SS1672 and SS2258. The coating, according to FIG. 2a, being composed of 6 κ-Al₂O₃ layers interspersed by layers of Ti(C,N), (total multi-layer thickness 7 μm) was tested on SS1672 and a coating deposited according to FIG. 2b, being composed of 5 κ-Al₂O₃ layers interspersed by layers of Ti(C,N) (total multi-layer thickness 7 μm) was tested on SS2258. Cutting tests were also conducted using inserts having single layers of Al₂O₃, TiN and Ti(C, N) as well as a multi-layer of κ-alumina and TiN were compared. The results are given in Tables 3 and 4. TABLE 3 SS1672, Cutting Speed 250 m/min Coating Life time/min Failure Mode Al₂O₃ 11 crater wear TiN 15 crater wear + notch TiCN 19 crater wear + notch Multi κ + TiN 25 crater wear Multi κ + TiCN 39 crater wear

[0029] TABLE 4 SS2258, Cutting Speed 200 m/min Coating Life time/min Failure Mode Al₂O₃ 15 flank wear TiN 8 crater wear TiCN 8 crater wear Multi κ + TiN 25 flank wear Multi κ + TiCN 32 flank wear

EXAMPLE 3

[0030] A detailed comparison of the behaviors of a single layer and a multi-layer coating (FIG. 2b) in turning SS2258, is presented in FIG. 3. The multi-layer coating is superior to the single layer SS2258. In this steel, the flank wear is clearly reduced by the Ti(C,N) coatings. It is clear from the SEM micrograph that both crater wear and flank wear resistance of the multi-layer κ-Al₂O₃ coated inserts were superior to those of the single κ-Al₂O₃ coated inserts. In this kind of steel where alumina-coated inserts in general perform well, the effects of the multi-layering is very clear. The lifetime of the insert is drastically increased, in particular at 200 m/min more than about 100%. In ball-bearing steel, SS2258 (hypereutectoid steel), a multi layering results in much more drastically reduced wear than observed earlier in hypoeutectoid steels (U.S. Pat. No. 5,700,569).

EXAMPLE 4

[0031] A detailed comparison of the behaviors of a single layer and a multi-layer coating (FIG. 2b) in turning of SS1672, is presented in FIG. 4. The multi-layer coating is superior to the single layer also in SS1672. Compared with miltilayer κ-Al₂O₃ coatings according to U.S. Pat. No. 5,700,569, mulitlayers of κ-Al₂O₃ with Ti(C,N) together with reduced thickness of the alumina layers enhanced the performance of the inserts over the prior art. It appears clear from the SEM micrograph that both crater wear and flank wear resistances were superior to those exhibited by the single layer. In this steel, the flank wear is clearly reduced more than earlier observed when multi-layer coatings of κ-Al₂O₃ and Ti(C,O) were investigated (U.S. Pat. No. 5,700,569).

[0032] The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention. 

1. A coated body wherein the coating comprises a multi-layer of γ-Al₂O₃.
 2. A coated body wherein the coating comprises a multi-layer of κ-Al₂O₃ applied by a chemical vapor deposition at a temperature of from 700 to 900° C.
 3. A coated body wherein the coating comprises a multi-layer of κ-Al₂O₃ and γ-Al₂O₃, each applied by a chemical vapor deposition at a temperature of from 700 to 900° C.
 4. The coated body of any of claims 1, 2 and 3 wherein the said multi-layers of γ- and/or κ-Al₂O₃ are interspersed with layers of Ti(C,N).
 5. The coated body of claim 4 wherein the multi-layers of γ and/or κ-Al₂O₃ comprise layers having a thickness of from about 0.1 about 3.2 microns.
 6. The coated body of claim 4 wherein the multi-layers of γ and/or κ-Al₂O₃ comprise layers having a thickness of from about 0.3 to about 1.2 microns.
 7. The coated body of claim 4 wherein the layers of Ti(C,N) comprise layers having a thickness of from about 0.1 to about 3.2 microns.
 8. The coated body of claim 4 wherein the layers of Ti(C,N) comprise layers having a thickness of from about 0.3 to about 1.2 microns.
 9. The coated body of any of claims 1, 2 and 3 wherein a layer of Ti(C,N) is atop the said multi-layers of γ and/or κ-Al₂O₃.
 10. The coated body of claim 3 wherein the γ-Al₂O₃ layers comprise the uppermost alumina layers and the κ-Al₂O₃ layers comprise the innermost alumina layers.
 11. The coated body of any of claims 1, 2, and 3 wherein the said multi-layers have a total thickness of from about 3 to about 30 microns.
 12. The coated body of claim 11 wherein the said multi-layers have a total thickness of from about 5 to about 15 microns.
 13. The coated body of any of claims 1, 2, and 3 wherein the said body is selected from the group consisting of a cemented carbide, cermet, ceramic, high speed steel and mixtures thereof.
 14. A metal cutting tool made from the coated body of claim
 13. 15. A coated body wherein the coating comprises a multi-layer of κ-Al₂O₃ and/or γ-Al₂O₃ layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N).
 16. A coated body wherein the coated comprises a multi-layer of κ-Al₂O₃ and/or γ-Al₂O₃ layers interspersed with layers of Ti(C,N) on a layer of Ti(C,N) and with a layer of Ti(C,N) atop of the said multi-layer. 